Quality of reception and especially frequency-modulated (FM) radio reception in vehicles is impaired by two major sources of disturbances: (1) multi-path reception; (2) ignition noise due to neighboring vehicles, and other ambient radio noise.
The reception conditions in movable vehicles change continuously. Thus, use of directional antennae, suitable with stationary installation and there substantially improving reception quality, is not generally possible. Rather, antennas for vehicles are designed to be essentially independent of direction, that is, to have reception sensitivity which is location-independent. It has previously been proposed to use receivers with a plurality of antennas in order to improve reception. The selection of which one of the antennas to be coupled to the receiver is usually based on field strength, that is, level of the signal appearing at any one of the antennas. This selection does not necessarily, however, connect the antennas with maximum signal-to-noise level to the receiver. Optimization of signal-to-noise level in the receiver thus is not ensured.